The use of radioisotopes as labels for substances normally present in the blood, which are known to be involved in active transport, and the use of drugs, metabolic inhibitors and specific inhibitors either topically or systemically will enable conclusions concerning the role of active transport in the functions of the blood-vitreous body barrier to be made. Intraocular localization of radioactive substances will be achieved by use of numerous thin slices (less than 1 mm) of the frozen intraocular fluids and tissues and by dissection of the separable components of each frozen slice. This experimental procedure, including short experimental times, will enable quantitative estimates of the permeability of various regions of the blood-vitreous body barrier to be made. Studies of the effect of time on the intraocular distribution of tracers used will permit decisions to be made on the relative role of diffusion, convection and flow in their distribution. Estimates of the transfer coefficients across the aqueous-vitreous body interface can also be made. The unique features of the proposed experimental method are: 1) Little or no disturbance of the eye prior to terminations of the experiment, i.e. studies can be made of transfer from blood to intraocular fluids and tissues at steady state. 2) Use of one eye of the animal as a control to study the effect of topically applied drugs. 3) The method for analyzing the data results in quantitative estimates of the relative permeabilities of various regions (posterior, central or anterior) of the blood-vitreous body barrier. The data is useful re: glaucoma and eye physiology.